Mechanical seal isolator

ABSTRACT

A mechanical seal isolator is provided in a submergible pump installation for protecting a mechanical seal from well fluid. The mechanical seal, which prevents well fluid from passing along a shaft to an oil-filled electric motor, may be located at the top of an oil-containing motor protector which is positioned between the pump and the motor or at the top of the motor itself. The mechanical seal isolator is interposed between the seal to be protected and the pump and contains a fluid of greater density than the well fluid and the oil in the protector or the motor and of sufficient quantity to surround and extend over the mechanical seal under all operating conditions of the motor.

United States Patent 1191 Dunbar MECHAPHCAL SEAL ISOLA TOR Clarence E.Dunbar, Bartlesville, Okla.

TRW, Inc., Cleveland, Ohio Inventor:

73 I Assignee:

1451 Dec. 10,1974

Primar Eramirrrr-l D. .\liller Assistant Examiner-Harpy E. Moose. Jr.Attorney, Agent, or Firm-Shapiro and Shapiro [57] ABSTRACT A mechanicalseal isolator is provided in a submergible pump installation forprotecting a mechanical seal from well fluid. The mechanical seal, whichprevents well fluid from passing along a shaft to an oil-filled electricmotor, may be located at the top of an oilcontaining motor protectorwhich is positioned between the pump and the motor or at the top of themotor itself. The mechanical seal isolator is interposed between theseal to be protected and the pump and contains a fluid of greaterdensity than the well fluid and the oil in the protector or the motorand of sufficient quantity to surround and extend over the mechanicalseal under all operating conditions of the motor.

8 Claims, 2 Drawing Figures PAIEMEB EM T 3.854.064

' SHEET 10F 2 FIG? PATENTEU 2 1 3354.064

1 SHEEI 2 0F '2 F/GI 2 1 MECHANICAL SEAL ISOLATOR BACKGROUND OF THEINVENTION This invention relates to submergible pump installations andis more particularly concerned with the protection of a mechanical sealwhich prevents well fluid from passing along a shaft to the drivingmotor.

'In the art of submergible pumps, which may be em ployed to pump oil orwater from a well, for example, it'is common practice to employ a pumpof the centrifugal type driven by an electric motor filled with oilwhich lubricates and cools the motor. Since the oil in the motor expandsand contracts, depending upon whether the motor is operating or at rest,it is also common practice to provide a motor protector of theoilfilled. type between the motor, and the pump or of the breathing bagtype in the motor to accommodate the expansion and to prevent theingress of corrosive well fluid to the motor when the oil contracts. Ina protector of the oil-filled type, an-arr'angement of chambers andpassages keeps an interface between the oil and the well fluid out ofthe electric motor. In the breather bag type of protector, a collapsiblediaphragm may be built into the lower end of the 'motor 'to accommodatechanges in volume of the oil in the motor; As long as the oil is notlost or contaminated and the mechanical seal on the shaft leading fromthe motor remains intact, well fluid is kept out of the motor.Oil-filled electric motors, motor protectors, and related apparatus aredisclosed, for example, inthe following U.S. patents:

REZtJ,783 2,674,702

1,701,468 2,739,252 2,979,347 l,970,484 2,740,058 3.l l6,432 2.236.887.2,783,400 3,l53.l60 2.270.666 2,854,595 3,384,769 2,674,194 2,922,0553,502,9l9

In U.S. Pat. No. Re. 26,783 and in U.S. Pat. No. 3,502,919 it isproposed to employ in a motor'protector a so-called intermediate'fluidbetween the ambient well fluid and the motor oil, the intermediate fluidhaving a higher'specific gravity than theambient well fluid and themotor oil and serving'to separate the well fluid from themotor oil in amanner intendedto prevent contamination of the motor oil by the wellfluid. However, a serious problem which has continued to exist in theprior art is that under conditions of normal operation the mechanicalseal which is located at the top of the protector (or which is at thetop of the motor, where a breather bag is used) 'and which is intendedto prevent the passage-of well fluid to'the motor along the shaftconnecting the pump andth emotor is exposed to the well fluid and henceis subject to corrosive and abrasive attack by the well fluid. The lifeof the me.- chanicalsealand the lifeof the electric motor itself arethus shortened, requiring that the entire pump installation be pulledfrom the well for repairs at an earlier time than would otherwise be thecase.

SUMMARY OF THE INVENTION I It is accordingly apr incipal object ofthepre sent' in vention f to provide a mechanical seal. isolatorwhichchanical seal isolator is interposed between the pump and astandard oil-filled motor protector, or between the pump and a motorhaving a breathing bag, without requiring modification of the pump, theprotector, or the motor.

Still another object of the invention is to provide a mechanical sealisolator which maintains a body of high density fluid around and abovethe mechanical seal under all operating conditions of a submergible pumpmotor.

Briefly stated, in accordance with a first embodiment of the invention amechanical seal isolator is provided between a standard oil-filledprotector of an oil-filled electric motor and a submergible pump drivenby the motor. The isolator includes a housing containing a shaft whichconnects the shaft of the motor protector with the shaft of the pump,the protector shaft also being connected to the shaft of the motor. Theisolator contains a quantity of high density fluid sufficient tosurround and extend above the mechanical seal at the top of theprotector duringall operating conditions of the pump installation. Aportion of the high density fluid extends into the motor protector also.Inaccordance with a second embodiment, the seal isolator is interposedbetween the pump and the motor and also maintains high density fluidaround and over the sea] at the top of the motor shaft, which is coupledto the shaft of the isolator.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE INVENTIONReferring to the drawings, and initially to FIG. 1, the invention willbe described in its application to a submergible pump installation 10comprising a submergible pump 12, an oil-filled electric motor 14, andan oilcontaining motor protector 16. Although only the right half of thefigure is shown in section, for purposes of the explanation of theinvention the left half may be assumed to be essentially the same. Thepump may be a conventional centrifugal type, such as the pump disclosedin US. Pat. No. 2,270,666 or U.S. Pat. No. 2,775,945, for example.Similarly, the motor may be a conventional type, such as the motordisclosed in U.S. Pat. No. 2,270,666 or U.S. Pat. No. 2,315,917, forexample, and the protector may be a standard type employed with such amotor. For purposes of illustration ofthe principles of the invention,the protector may be assumed to be a protector of the type disclosed inU.S. Pat. No. 2,783,400. lnterposed'between the pump 12 and theprotector16 is the mechanical seal isolator 18 of the invention. Y Y I Themechanical seal isolator comprisesa housing 20 which may be bolted orsecured by'thre ads to the pump 12 at the upper end and-to the protector16 at the lower end. As shown, the mechanical seal isolator has a pairof bearings 22 and 24 adjacent to the opposite ends thereof forrotatably supporting a shaft section 26 along the axis of the isolatorhousing. The shaft is provided with splined ends 28 and 30 which arecoupled to similarly splined ends of corresponding shaft sections of theprotector and the pump by means of couplings, one of which is shown at32. The lower end 34 of the protector shaft section is similarly coupledto the upper end of a shaft section of the motor 14. It is apparent thatwhen the components of the submergible pump installation have beenassembled, a coaxial or colinear arrangement is provided of the generaltype disclosed in U.S. Pat. No. 2,315,917 or U.S. Pat. No. 2,775,945(but without the mechanical seal isolator of the present invention).

The interior of the housing of the isolator provides a chamber 36 forcontaining fluid, and the spiders or transverse partitions 38 and 40which support the bearings of the shaft section 26 are provided withpassages such as 42 and 44 for the fluid. A drain and fill valve 46 isprovided for initial filling (or draining) of the chamber 36.

As shown, the motor protector has a conventional mechanical seal 48located in a top portion of its housing, theseal surrounding its shaftsection 50 adjacent to the upper end thereof. Such seals, which are wellknown in protectors of the type referred to, have been employedheretofore to prevent well fluid from passing along the shaft section 50to the motor 14. If well fluid enters the motor, it is likely thatserious damage to the motor will ensue because of the corrosive and/orabrasive nature of the well fluid. To repair this damage, it isnecessary to pull the entire installation from the well. Althoughstandard motor protectors will accommodate expansion of the oil in themotor which occurs when the motor operates and will normally contain asuffiwill eventually migrate along the shaft into the motor,

a highly undesirable condition, as stated.

In accordance with the present invention, the mechanical seal 48 isisolated from the well fluid, and protected from the deleterious effectsof the well fluid, for all operating conditions of the motor, that is,whether the motor is runnning or at rest. Hence, the useful life of themechanical seal is substantially lengthened. This is accomplished byproviding in the chamber 36 a fluid of greater density and specificgravity than the well fluid and than the oil in the protector and insufflcient quantity to be in surrounding contact with and to extendabove mechanical seal 48 under all operating conditions of the motor. Asdescribed in U.S. Pat. No. 2,783,400, chamber 52 of the protector isfilled with protector oil. When the oil in the motor expands, it forcesoil along a'passage indicated at 54 surrounding the shaft section 50 toopenings (not shown) into the chamber 52 at the upper end thereof,forcing oil' in the chamber 52 up a conduit 56 which extends from apoint adjacent to the lower end of chamber 52 to the region of, themechanical seal 48 (and preferably above the seal). In theabsence of themechanical seal isolator of the invention, the oil in the protector willthen move upwardly into the lower portion of the pump housing. However,when the motor has stopped running and the oil has contracted, wellfluid will move downwardly from the pump housing into the region of themechanical seal and into the conduit 56.

In accordance with the present invention, on the other hand, heavy dutyfluid 58 from housing 20 surrounds and extends above sea] 48 at alltimes, filling the conduit 56 and the lower portion of chamber 52 in theprotector at all times. This high density fluid 58, which may be SeriesE Freon (Dupont), for example, rises in chamber 52 of the protector to alevel such as indicated by line 60 when the motor is idle, withconcurrent lowering of the level of the high density fluid in chamber 36of the isolator, as indicated by line 62. When the motor is running, theexpansion of the oil in the motor and the protector forces the highdensity fluid in chamber 52 down, as indicated by line 64, and up inchamber 36, as indicated by line 66. It is thus apparent that themechanical seal 48 is fully protected from contact with the well fluid.To prevent agitation of the heavy duty fluid in the chamber 36 a shafttube 68 is employed, a thin layer of heavy duty fluid being presentbetween the tube 68 and shaft section 26.

FIG. 2 illustrates a second embodiment of the invention, in which themechanical seal isolator (essentially the same isolator described withreference to FIG. 1) is interposed between the pump 12' and the motor14. The lower end 30 of the shaft section 26 of the isolator is coupledto the upper end of a shaft section 70 of the motor, while the upper end72 of the shaft 26 is coupled to the lower end of shaft section 74 ofthe pump. The housing of the isolator 18 is bolted to the housing of themotor and the housing of the pump in the form shown.

The motor is a conventional type having a breathing bag or diaphragm 76at the lower end thereof. Such motors are disclosed, for example, inU.S. Pat. Nos. 2,674,702; 2,974,240; and 2,979,347. A conventionalmechanical seal 78 surrounds shaft section 70 at the top of the motor toprevent ingress of external fluid to the interior of the motor, which isfilled with oil.

The pump 12', which may be of a conventional centrifugal type as notedpreviously, has a mechanical seal 80 surrounding the pump shaft section74 to prevent well fluid from entering the interior of the lower chamber82 of the pump housing, which contains a breathing diaphragm 84, oneside of which is exposed to the well fluid, as is the case withdiaphragm 76.

In the embodiment of FIG. 2, heavy duty fluid fills the chamber 36 ofthe isolator, fills the chamber 82 of the pump, and extends downwardlythrough passage 42 so as to surround the mechanical seal 78 at the topof the motor 14'. Thus, even if well fluid leaks past the seal 80, themechanical seal 78 will be isolated from the well fluid by the heavyduty fluid, expansion and contraction of which is accommodated by thebreathing diaphragm 84.

The mechanical seal isolator of the invention may be used with standardpumps, protectors, and motors without requiring modification of any ofthese components. The isolator allows normal operation of the mechanicalseal and any pressure balancing means which may be present. The heavyduty fluid will surround the seal even if over expansion causes loss ofmost of the fluid. Moreover, the heavy duty fluid has higher heattransfer capabilities than the fluids which would otherwise contact theseal, further contributing to extended seal life.

While preferred embodiments of the invention have been shown anddescribed, it will be apparent to those skilled in the art that changescan be made in these embodiments without departing from the principlesand spirit of the invention, the scope of which is defined in theappended claims.

The invention claimed is:

1. In a submergible pump installation, a rotary pump having a pump shaftsection, means including an oilfilled electric motor for driving saidpump, said driving means having a shaft section provided with amechanical seal for preventing the pumped fluid from passingtherethrough to said motor, and a mechanical seal isolator comprising ahousing interposed between said driving means and said pump and having ashaft section connecting said shaft section of said pump to said shaftsection of said driving means, said housing having a chamber thereincommunicating with said seal adjacent to one end of the housing, saidchamber containing a fluid of greater density than said fluid to bepumped and said oil, said greater density fluid being in surroundingcontact with said mechanical seal under all operating conditions of saidmotor, irrespective of the expansion and contraction of the oil in saidmotor.

2. An installation in accordance with claim 1, wherein said chambercommunicates with said pump adjacent to the end of the said housingwhich is opposite said one end.

3. An installation in accordance with claim 2, wherein said housing ofsaid mechanical seal isolator has bearing means disposed adjacent to theends thereof for supporting the associated shaft section coaxiallytherewith, said bearing means having fluid passages associated therewithfor conducting fluid in said chamber past said bearing means, and saidshaft section in said housing having coupling means at the ends thereoffor coupling the last-mentioned shaft section to the shaft sections ofsaid pump and said driving means, said housing having means forconnecting the same to said pump and to said driving means.

4. An installation in accordance with claim 1, wherein said drivingmeans comprises an oil-containing motor protector interposed betweensaid motor and said isolator, said protector having a housing with saidseal located in a top portion thereof, said protector having a chambertherein with an upper end below said seal, said protector having aconduit extending from a point above said seal to a point in saidprotector chamber adjacent to the lower end thereof and having a passagefor introducing oil at a point in said protector chamber adjacent to theupper end thereof when the oil in said motor expands, said greaterdensity fluid filling said conduit and occupying a portion of saidprotector chamber adjacent to said lower end.

5. An installation in accordance with claim 1, wherein said motor has ahousing with said seal located in a top portion thereof, said sealisolator having the lower end of its housing connected to the upper endof the motor housing, said motor having breathing diaphragm means foraccommodating expansion and contraction of the oil in said motor.

6. An installation in accordance with claim 5, said pump having ahousing with a chamber at the lower end connected to the upper end ofthe seal isolator chamber and containing said greater density fluid.

7. An installation in accordance with claim 6, wherein said pump hasbreathing diaphragm means for accommodating expansion and contraction ofsaid greater density fluid.

8. An installation in accordance with claim 1, wherein saidisolator hasa tube surrounding the shaft section of said isolator to preventagitation of said greater density fluid.

1. In a submergible pump installation, a rotary pump having a pump shaftsection, means including an oil-filled electric motor for driving saidpump, said driving means having a shaft section provided with amechanical seal for preventing the pumped fluid from passingtherethrough to said motor, and a mechanical seal isolator comprising ahousing interposed between said driving means and said pump and having ashaft section connecting said shaft section of said pump to said shaftsection of said driving means, said housing having a chamber thereincommunicating with said seal adjacent to one end of the housing, saidchamber containing a fluid of greater density than said fluid to bepumped and said oil, said greater density fluid being in surroundingcontact with said mechanical seal under all operating conditions of saidmotor, irrespective of the expansion and contractioN of the oil in saidmotor.
 2. An installation in accordance with claim 1, wherein saidchamber communicates with said pump adjacent to the end of the saidhousing which is opposite said one end.
 3. An installation in accordancewith claim 2, wherein said housing of said mechanical seal isolator hasbearing means disposed adjacent to the ends thereof for supporting theassociated shaft section coaxially therewith, said bearing means havingfluid passages associated therewith for conducting fluid in said chamberpast said bearing means, and said shaft section in said housing havingcoupling means at the ends thereof for coupling the last-mentioned shaftsection to the shaft sections of said pump and said driving means, saidhousing having means for connecting the same to said pump and to saiddriving means.
 4. An installation in accordance with claim 1, whereinsaid driving means comprises an oil-containing motor protectorinterposed between said motor and said isolator, said protector having ahousing with said seal located in a top portion thereof, said protectorhaving a chamber therein with an upper end below said seal, saidprotector having a conduit extending from a point above said seal to apoint in said protector chamber adjacent to the lower end thereof andhaving a passage for introducing oil at a point in said protectorchamber adjacent to the upper end thereof when the oil in said motorexpands, said greater density fluid filling said conduit and occupying aportion of said protector chamber adjacent to said lower end.
 5. Aninstallation in accordance with claim 1, wherein said motor has ahousing with said seal located in a top portion thereof, said sealisolator having the lower end of its housing connected to the upper endof the motor housing, said motor having breathing diaphragm means foraccommodating expansion and contraction of the oil in said motor.
 6. Aninstallation in accordance with claim 5, said pump having a housing witha chamber at the lower end connected to the upper end of the sealisolator chamber and containing said greater density fluid.
 7. Aninstallation in accordance with claim 6, wherein said pump has breathingdiaphragm means for accommodating expansion and contraction of saidgreater density fluid.
 8. An installation in accordance with claim 1,wherein said isolator has a tube surrounding the shaft section of saidisolator to prevent agitation of said greater density fluid.